Brake system and method

ABSTRACT

A system for adjusting a brake force to be applied by a brake includes a module for estimating a weight of a vehicle to which a brake is fitted, a module for determining an angle of incline upon which the vehicle is positioned, and a control unit for calculating a sufficient brake force to be applied according to predetermined criteria based upon the estimated weight and the incline to maintain the vehicle in a stationary state. The control unit is configured to signal the brake to apply the calculated amount of force.

REFERENCE TO RELATED APPLICATION

This application claims priority to United Kingdom Patent ApplicationNo. 0802212.1 filed Feb. 6, 2008.

BACKGROUND OF THE INVENTION

The present invention relates generally to a brake system and method.More particularly, the present invention relates to a system configuredto estimate a change in temperature of a brake component, a method ofestimating the change in temperature of the brake component, and asystem and method for applying a parking brake.

Standard braking systems for heavy vehicles, such as trucks, buses andcoaches, include air actuated service brakes at each wheel of thevehicle including a membrane type brake chamber biased into a brake offcondition, and brakes operable as service and parking brakes on somewheels (e.g., the rear wheels of a tractor unit of an articulated truckand trailer unit). Such combined brakes also include a membrane type airchamber. Behind that, a parking brake chamber is biased into a parkingbrake-on condition by a spring, but while the vehicle is in motion, isheld in the off position by pressurized air introduced into thecylinder. To apply the parking brake, the air is vented, permitting thespring to extend and apply the brake. Such spring brakes maintain a highparking brake force even if the brake disc shrinks due to cooling.

It is desirable to replace the parking brake cylinder by an alternativeapparatus of applying the parking brake that is more compact and reducesthe amount of components in the vehicle's air supply system. To thisend, the present applicant has proposed a number of alternative parkingbrake devices that utilize electromechanical components, such aselectric motors, to apply the parking brake (see for example EP1596089and EP1596090).

It has now been recognized by the present applicant that one problemwith such parking brakes (and with standard spring parking brakes) isthat they fully apply the parking brake at its maximum possible force,even if the particular conditions under which the vehicle is to bemaintained stationary do not require such a high force to be used. Thisplaces the components of the brake, such as the caliper, the operatingshaft and the pistons, under unnecessary stress, thus shortening thelife of the brake. This problem is particularly acute for applicationssuch as buses, where for instance the parking brake is automaticallyapplied each time the passenger door is opened.

A further problem with known electromechanical parking brakes is thatthey may, under some circumstances, be unable to account for anyshrinkage of brake components, primarily brake discs. Shrinkage mayoccur as such components cool while a vehicle is parked, followingheating that has been frictionally induced by use of the service brakewhen the vehicle is in motion. If an insufficient parking brake force ismaintained after cooling, there is a danger the vehicle may roll away.An additional problem is how to implement such an electromechanicalsystem, including its control in a safe and low cost manner.

The present invention seeks to overcome, or at least mitigate, theproblems of the prior art.

SUMMARY OF THE INVENTION

One aspect of the invention provides a system configured to estimate achange in temperature of a brake component of a vehicle brake during abraking operation, The system includes a weight estimation module forestimating a weight of a vehicle to which the brake is fitted, and avolume estimation module for estimating a volume of the brake component.The system also includes a temperature model module for calculating achange in temperature during brake application based on a relationshipbetween the weight of the vehicle as estimated by the weight estimationmodule, the volume of the brake component as estimated by the volumeestimation module, the deceleration of the vehicle, and furtherconstants of the vehicle and/or the brake.

A second aspect of the present invention provides a method of estimatinga change in temperature of a brake component of a vehicle brake during abraking operation. The method includes the steps of estimating a weightof a vehicle to which a brake is fitted, estimating a volume of thebrake component, and calculating a change in temperature of the brakecomponent based upon the change in velocity of the vehicle, theestimated weight of the vehicle, the estimated volume of the brakecomponent, and further constant values of the brake.

A third aspect of the present invention provides a system for adjustinga brake force to be applied by a brake including a module for estimatinga weight of a vehicle to which the brake is fitted, a module fordetermining an angle of incline upon which the vehicle is positioned,and a control unit for calculating a sufficient brake force to beapplied according to predetermined criteria based upon the estimatedweight and the determined angle of incline to maintain the vehicle in astationary state. The control unit is configured to signal the brake toapply the calculated amount of force.

A fourth aspect of the present invention provides a method for adjustinga brake force to be applied by a brake. The method includes the steps ofestimating a weight of a vehicle to which the brake is fitted,determining an angle of incline upon which the vehicle is positioned,calculating a sufficient brake force to be applied according topredetermined criteria based upon the estimated weight and thedetermined angle of incline to maintain the vehicle in a stationarystate, and signalling the brake to apply the calculated amount of force.

A fifth aspect of the present invention provides an electromechanicalparking brake system for a heavy vehicle braked by air-actuated servicebrakes. The system includes an EPB-ECU and a first electromechanicalparking brake actuator controlled by the EPB-ECU. The system furtherincludes a redundant sub-system for applying a second parking brake inthe event of a failure in the EPB-ECU or the first electromechanicalparking brake actuator.

A sixth aspect of the present invention provides an electromechanicalparking brake system for heavy vehicles including a tractor unit and atrailer unit. The system includes a user input device and a controller.The controller is configured upon receiving a signal corresponding to apredetermined user input from the user input device to enter a test modein which the controller signals release of a brake on the trailer unitand to maintain or apply a parking brake on the tractor unit such that avehicle user can determine whether the parking brake of the tractor unitalone is capable of holding the tractor unit and the trailer unit.

A seventh aspect of the present invention provides a method of testingwhether the parking brakes of a tractor unit of a heavy vehicle having atractor and trailer combination can hold the combination. The methodincludes the steps of a vehicle user carrying out a predetermined inputto an electromechanical parking brake system, a controller of theelectromechanical parking brake system signalling release of the brakesof the trailer in response to the input, and the controller signallingthe return to normal operation of the electromechanical parking systemin response to a further predetermined user input or after apredetermined timeout delay.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a known brake system for a tractor unitof a heavy vehicle;

FIG. 2 is a schematic diagram of a brake system for a tractor unit of aheavy vehicle according to a first embodiment of the present invention;

FIG. 3A is a schematic diagram of a control circuit for the brake systemof FIG. 2;

FIG. 3B is a schematic diagram of a variant of the control circuit ofFIG. 3A;

FIG. 4 is a schematic diagram of an alternative control system for thebrake system of FIG. 2;

FIGS. 4A to 4F are schematic diagrams illustrating further controlsystem layouts;

FIGS. 5 and 6 are diagrams illustrating the relationship between forceand time for various braking situations;

FIG. 7 is a flow chart illustrating the function of a load estimationmodule of a system according to the present invention;

FIG. 8 is a flow chart for obtaining a calculated disc volume of a brakedisc;

FIGS. 9 and 10 are two further diagrams illustrating the change in forceover time for further braking operations in accordance with anotherembodiment of the present invention; and

FIG. 11 is a schematic diagram of the control system function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, a braking system 10 of a tractor unit 1 of anarticulated truck is shown schematically. The system includes an airsupply portion 12, a service brake portion 14, a parking brake portion16, and a trailer control portion 18. The layout of such a system iswell known to those skilled in the art, but for convenience, the primecomponents are briefly described below. The thinner connecting linesdenote air connections, and the thicker connecting lines electricalconnections.

The air supply portion 12 includes an air compressor 20 connected to apressure regulator 22, an air dryer 24 having its own regenerationreservoir 26, a four circuit protection valve 28, and three airreservoirs 30 a, 30 b and 30 c each with an associated water releasevalve 32 a, 32 b, and 32 c. The supply lines from the air reservoirs 30a and 30 c are further connected to a double pressure sensor 34. Thedouble pressure sensor 34 enables the pressures in the supply lines fromthe two air reservoirs 30 a and 30 c to be compared to check forproblems, such as leaks.

A pair of pressure switches 36 a and 36 b are also connected to the airlines from the air reservoirs 30 a and 30 c and provide an electricaloutput to a pressure warning lamp 38 via an electrical circuit, shown inthicker lines. Finally, a pressure switch 37 and a pressure warning lamp39 are connected to the air supply line to the parking brake.

The service brake portion 14 includes a service brake valve 40 connectedto a driver's brake pedal 42, a load sensitive brake force meter 44,service brake cylinders 46 a and 46 b for the brakes connected to afront axle of the tractor unit 1, and service brake portions 48 a and 48b of a combined parking and service brake cylinders 50 a and 50 bconnected to a rear axle of the vehicle.

The parking brake portion 16 includes a parking brake valve 52 connectedto a parking brake lever 54 operable by the driver to apply the parkingbrake. The parking brake valve 52 is connected via a relay valve 56having overload protection to a non-return valve 58 and to springparking brake portions 60 a and 60 b of the combined park and servicebrake cylinders 50 a and 50 b.

The trailer control portion 18 includes a trailer control valve 62 andconnections to connect trailer air lines thereto. This would, of course,be omitted from heavy vehicles that do not tow a trailer, such as buses.

With reference to FIG. 2, a brake system according to an embodiment ofthe present invention is illustrated, with parts similar to those ofFIG. 1 labelled 100 higher. Only those parts that differ from FIG. 1 arediscussed in detail below.

In FIG. 2, the air supply portion 112 is substantially unchanged fromFIG. 1, except that there is no equivalent of the air reservoir 30 b andthe corresponding water release valve 32 b. Likewise, the service brakeportion 114 is similar except that the service brake valve 140 has anadditional electrical service brake valve actuator 166, described inmore detail below. Due to the deletion of one air reservoir, a smallercompressor 120 can be provided.

In contrast, the parking brake portion 116 is fundamentally altered. Theparking brake portion 116 no longer uses any form of pressurized airfrom the air supply portion 112 and now operates solelyelectromechanically. At the heart of the parking brake portion 116 is anelectric parking brake electronic control unit module (hereinafter“EPB-ECU”) 164, which is shown in more detail in FIG. 3A. The EPB-ECU164 is connected to the service brake valve actuator 166 at the servicebrake valve 140, as discussed above, to a valve actuator 167 at thetrailer control valve 162 such that electrical signals therefrom mayopen and close these valves in response to signals from the EPB-ECU 164.As a result, the EPB-ECU 164 may also apply the service brake andparking brakes of a trailer (not shown) if connected to the tractor unit101.

Trailer parking brakes would normally be standard spring-type brakesirrespective of electromechanical parking brakes being used on thetractor unit.

In addition, the EPB-ECU 164 has outputs to electromechanical parkingbrakes 168 a and 168 b for each of the rear wheels of the tractor unit.The EPB-ECU 164 receives an input from a parking brake lever 170 mountedin a cab of the tractor unit 101. Some or all of these connections mayoccur over a Controller Area Network (CAN) bus provided in the vehicle,by direct wiring, or by another suitable kind of communication (forexample, a short range radio link).

FIG. 3A illustrates one embodiment of the EPB-ECU 164 which includes asingle ECU 172 drawing its power from a single 12V battery 174 a of atwo battery power supply that further includes a second battery 174 b.The ECU 172 receives driver demand inputs from a parking brake lever 170and a “hill-hold” button 186. The ECU 172 further receives inputs via aCAN bus 173 from the following sensors: a brake pedal switch 188, aninclinometer 190, a sensor on the load sensitive brake force meter 192,an ignition switch sensor 193, an ambient temperature sensor 194(typically present in air conditioning systems), a seat belt sensor 195,an engine torque sensor 196, a brake torque sensor, a retarder torquesensor 198, and wheel speed sensors 199 (from the vehicle ABS/EBDsystem). In some embodiments, the inclinometer 190 can be part of theEPB-ECU 164.

The ECU 172 has outputs to first and second motors 176 a and 176 b,respectively, of the electromechanical parking brakes 168 a and 168 b onthe rear axle of the tractor unit. The parking brakes are arranged toclamp the discs 169 a and 169 b. In alternative embodiments, the parkingbrakes 168 a and 168 b may be provided on a front axle of the vehicle.In this configuration, the parking brake can act as a secondary brake inthe event of a failure in the air supply to the service brake, thusfulfilling the requirements of ECE 13 (“uniform provisions concerningthe approval of vehicles of categories M, N and O with regard tobraking”).

The ECU 172 has a further output to the service brake valve actuator166, for the service brake valve 140, and the valve actuator 167 of thetrailer control valve 162. In addition, it has the following outputs toindicate its status to the driver: a failure light 178, an activity lamp180, an audible warning buzzer 182, and a demand switch lamp 184. TheECU 172 is programmed to apply the parking and/or service brakes inresponse to inputs from the parking brake lever and various sensorsprovided in the vehicle in accordance with various algorithms as set outbelow.

However, it is desirable to use the system of FIGS. 2 and 3A only whenan alternative back-up for the parking brake function is available, suchas a suitable gearbox lock or spring brakes on the other axle (or insome instances, the same axle), since there is no redundancy within theEPB-ECU 164 itself, should a malfunction occur.

FIG. 3B shows a variant of the FIG. 3A system in which a single ECU 172a controls electromechanical parking brakes 168 a and 168 b on a frontaxle of a vehicle and electromechanical parking brakes 168 c and 168 don the rear axle of a vehicle. The parking brakes 168 a and 168 b arecontrolled directly in the same way as in FIG. 3A.

The parking brakes 168 c and 168 d on the rear axle are, however,controlled by “smart” actuators incorporating their own localcontrollers 175 a and 175 b on a separate channel of the ECU 172 ahaving its own power supply. The local controllers 175 a and 175 bcontain the necessary EPB logic and/or can provide feedback on achievedclamp or compliance force and fault state to the master and slavecontrollers. The connection of this second channel may be via a CAN orprivate bus. As a result, the supply of power to the actuator motors 176c and 176 d is controlled by the controllers 175 a and 175 b.

The controllers 175 a and 175 b are also connected via the CAN/privatebus to a gearbox controller of the vehicle (not shown). If the ECU 172 afails, the gearbox controller takes over control of parking brakes 168 cand 168 d and is thus able to provide a “failure mitigating” emergencyfunction on one of the two axles.

An alternative EPB-ECU 164′ is shown in FIG. 4 in which a master ECU172′, having the same associated components (all labelled as in FIG. 3A,but with a ′ suffix) is provided with a further slave ECU 172″, againhaving identical associated components (in this case identicallylabelled as in FIG. 3, but with the suffix ″). The master ECU 172′, isconnected to motors 176 a′ and 176 b′ on the front axle of the vehicle101, whereas the slave ECU 172″ is connected to parking brake motors 176a″ and 176 b″ mounted on a rear axle of the vehicle 101 (or vice-versain other embodiments). Certain components shown in FIG. 3 are notrepresented in FIG. 4 for reasons of clarity, but are neverthelesspresent.

The master ECU 172′ is independently connected to the CAN bus from theslave ECU 172″. The slave ECU 172″ is connected to the second battery174 b. Both ECUs 172′ and 172″ are identically programmed. Under normaloperation, only if both the master and the slave ECUs 172′ and 172″detect a driver demand from the parking brake lever 170 or other inputsover the CAN bus, and after positive match of their outputs, theappropriate signals are sent to the parking brake motors 176 a′, 176 b′,176 a″, 176 b″, the trailer control valve actuator 167, and the servicebrake valve actuator 166. The EPB-ECU 164 is configured such that onlyif one CAN bus connection fails or one battery fails will thefunctioning ECU alone signal a parking brake actuation on a single axle(albeit with a reduced ability to hold the vehicle). As a result, theEPB-ECU 164′ of FIG. 4 can be said to be “failure mitigating.”

FIGS. 4A to 4F illustrate further variations on the control systemlayout that provide various degrees of fault tolerance in the event ofsystem malfunctions. Like parts are, where possible, denoted by likenumerals as in FIGS. 3A to 4, but with the prefix ‘5’ instead of ‘1’.The smart parking brake controller and/or gearbox controller and/or EBScontroller may constitute the EPB-ECU discussed above and may receiveinputs from some or all of the sensors discussed above in relation toFIGS. 3A to 4 and some or all of the outputs to indicate the status ofthe system as discussed above in FIGS. 3A to 4.

In FIG. 4A, the parking brakes 569 a and 569 b are provided with EPBactuators 576 a and 576 b incorporating “smart” EPB actuator controllers575 a and 575 b. Each controller 575 a and 575 b is powered via powerconnections 583 from separate batteries 574 a and 574 b. A gearboxcontroller 577 of a gearbox 579 is also powered by one first battery 574a.

The gearbox is connected to a gear stick 553. The gear stick 553 isconfigured to be operable as a back-up parking brake demand input. Thisis achieved by a predetermined gear stick position (optionally inconjunction with an input from an ignition switch) being interpreted asparking brake demand. For example, there may be a specific “park”position. Alternatively, first gear plus ignition off and/or neutralplus ignition off may be interpreted as parking brake demand. An EBScontroller 587 is powered by the second battery 574 b.

A private CAN bus 573 enables the gearbox controller to communicate withthe first EPB actuator controller 575 a, and a further private CAN busenables the EBS controller 587 to communicate with the second EPBactuator 575 b. The EBS controller 587 is hardwired to a “smart” parkingbrake demand switch 554 incorporating a smart parking brake controller555 by a connection 581.

High speed (HS) CAN buses 571 enable the gearbox controller 577 and theEBS controller 587 to signal a display 585 in the vehicle cab to showappropriate status indications.

In this embodiment, the smart parking brake controller 555 acts as the“master” ECU in normal operation. Alternatively, the EBS controller 587may act as the master ECU. Either the EBS controller 587 or the gearboxcontroller 577 may act as a slave ECU in normal operation, but becomemaster if the smart parking brake controller 555 or the park brakedemand switch 554 fail.

The degree of fault tolerance provided by the system is illustrated bythe table below.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 1 Second battery or power supply faulty (open circuit) 1First/Second battery or power supply faulty (short 1 circuit) HS-CANfailure (open circuit to one ECU) 1 HS-CAN failure (open circuit to allECUs) 1 HS-CAN failure (short circuit) 1 Private-CAN failure (opencircuit to one ECU) 1 Private-CAN failure (short circuit) 1 Master ECUfailure (Smart EPB switch or EBS) 1 Slave ECU failure (EBS or Gearbox) 1Actuator failure 1

Thus, except in the instance of a complete power supply failure, atleast one EPB actuator remains operable to provide a parking brakefunction.

It is also important to note that by having multiple parking brakedemand inputs, the failure of, for example, the parking brake demandswitch 554 itself, as well as the associated controller 555, does notprevent the driver indicating to a functioning ECU the need for parkingbrake operation. By using the gear stick 553 as the back-up demandinput, this can be implemented without adding significantly to the cost.

FIG. 4B illustrates a variant of the system illustrated in FIG. 4A. Inthis embodiment, the EPB switch is no longer hard wired to the EBScontroller 587. By contrast, it is connected to the display 585 by aHS-CAN 571 and to the first smart EPB controller 575 a by a private CAN.The EBS controller 587 is no longer connected to the second smart EPBcontroller 575 b. The gearbox controller 577 is connected via a privateCAN in its place.

In this embodiment, either the smart parking brake controller 555 or theEBS controller 587 may be the master ECU. Either the EBS controller 587or the gearbox controller 577 may be the slave ECU.

The degree of fault tolerance provided by the system of FIG. 4B issimilar to that of FIG. 4A, as illustrated by the table below.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 1 Second battery or power supply faulty (open circuit) 1First/Second battery or power supply faulty (short 1 circuit) HS-CANfailure (open circuit to one ECU) 1 HS-CAN failure (open circuit to allECUs) 1 HS-CAN failure (short circuit) 1 Private-CAN failure (opencircuit to one ECU) 1 Private-CAN failure (short circuit) 1 Master ECUfailure (Smart EPB switch or EBS) 1 Slave ECU failure (EBS or Gearbox) 1Actuator failure 1

The embodiment of FIG. 4C is similar to FIG. 4B, except that the powersupply lines 583 from the first and second batteries are connectedrather than being independent. Diodes 557 are included in the lines 583to provide some protection against short circuits or other failures ofthe batteries. However, the trade-off of this arrangement is lesstolerance to faults in the supply cables. Thus, its desirability dependsupon whether battery or supply cable failure is deemed to be a greaterrisk.

The degree of fault tolerance this provides is illustrated in the tablebelow.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 1 Second battery or power supply faulty (open circuit) 1First/Second battery or power supply faulty (short 1 circuit) Powersupply (short circuit in supply coupling) 0 HS-CAN failure (open circuitto one ECU) 1 HS-CAN failure (open circuit to all ECUs) 1 HS-CAN failure(short circuit) 1 Private-CAN failure (open circuit to one ECU) 1Private-CAN failure (short circuit) 1 Master ECU failure (Smart EPBswitch or EBS) 1 Slave ECU failure (EBS or Gearbox) 1 Actuator failure 1

The embodiment of FIG. 4D utilizes a bus coupler 559 in the form of anormally closed relay at the smart parking brake controller 555 to sharepower between the smart parking brake controller 555 and the gearboxcontroller 577. The coupler also joins the private CAN 573 between thetwo smart EPB controllers 575 a and 575 b and between the smart parkingbrake controller 555 and gearbox controller 577. Provided either thesmart parking brake controller 555 or the gearbox controller has power,the relay 559 is held open (and they are able to operate their connectedactuators using the HS-CAN 571 via the display 585). If the smartparking brake controller 555 fails, but the left power supply remainsintact, the relay 559 closes and both actuators 576 a and 576 b areoperational via the gearbox controller 577. If the gearbox controller577 fails, the relay 559 closes and the other actuator control is takenover by the smart parking brake controller 555. The arrangement of FIG.4D also protects against failure in the private CAN; one instance ofdamage only will cause one actuator 576 a or 576 b to be inoperable.

As a consequence, it is possible for both parking brake actuators toremain operable for a number of potential faults, as set out in thetable below.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 1 Second battery or power supply faulty (open circuit) 1First/Second battery or power supply faulty (short 1 circuit) HS-CANfailure (open circuit to one ECU) 2 HS-CAN failure (open circuit to allECUs) 2 HS-CAN failure (short circuit) 2 Private-CAN failure (opencircuit to one ECU) 1 Private-CAN failure (short circuit) 1 Master ECUfailure (Smart EPB switch or EBS) 2 Slave ECU failure (EBS or Gearbox) 2Actuator failure 1

In FIG. 4E, the layout is a combination of the features of FIGS. 4C and4E, except that the power supply connection is replaced by a hard-wiredconnection 581 between the smart parking brake controller 555 and thegearbox controller 577. This enables both EPB actuators to remainoperable over a still wider range of potential faults as set out in thetable below. Specifically, in FIG. 4E now both the smart parking brakecontroller 555 and the gearbox controller 577 can actively assume thecontrol of the actuator 576 a and 576 b that it would not normallycontrol, in the event of a range of failures. The power supply to bothactuators 576 a and 576 b is widely ensured, with only a short circuitto ground in the power line causing a complete system failure.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 2 Second battery or power supply faulty (open circuit) 2First/Second battery or power supply faulty (short 2 circuit) Powersupply (short circuit in supply coupling) 0 HS-CAN failure (open circuitto one ECU) 2 HS-CAN failure (open circuit to all ECUs) 2 HS-CAN failure(short circuit) 2 Private-CAN failure (open circuit to one ECU) 1Private-CAN failure (short circuit) 1 Master ECU failure (Smart EPBswitch or EBS) 2 Slave ECU failure (EBS or Gearbox) 2 Actuator failure 1

FIG. 4F provides a still greater degree of redundancy in the system byproviding an active power supply coupler 561 that enables a singlebattery 574 a or 574 b to power all the critical system components inthe event of a failure of the other battery, so at least one actuator576 a and 576 b remains operable. The supply coupler 561 is held openwhen the system operates normally, but is configured such that it may beclosed actively by either the smart parking brake controller 555 or thegearbox controller 577 if there is no power available to the portion ofthe system normally powered by one of the batteries, to re-establishpower to that side. Thus, with this arrangement, some degree of parkingfunction (with at least one actuator) is retained for all the potentialfaults listed in the table below.

No. of Operable Fault EPB Actuators First battery or power supply faulty(open circuit) 2 Second battery or power supply faulty (open circuit) 2First/Second battery or power supply faulty (short 2 circuit) Powersupply (short circuit in supply coupling) 1 HS-CAN failure (open circuitto one ECU) 2 HS-CAN failure (open circuit to all ECUs) 2 HS-CAN failure(short circuit) 2 Private-CAN failure (open circuit to one ECU) 1Private-CAN failure (short circuit) 1 Master ECU failure (Smart EPBswitch or EBS) 2 Slave ECU failure (EBS or Gearbox) 2 Actuator failure 1

The control systems of FIGS. 4A to 4F enable an EPB system that utilizesa gearbox controller 577 as a slave ECU, but become the master ECU inthe event of failure of the usual master to comply with ECE Regulation13. Without such a failure mitigating system, the use of the gearboxcontroller as fall back for the park brake in trucks would not complywith this regulation. This is because a second failure mitigating slavecontroller alone is not sufficient. The communication, the power supply,and the demand inputs need to be failure mitigating as well. Thedifferent system layouts described about enable a selection to be madeabout what potential failures can be tolerated by the system, balancedagainst the cost of such a system.

The electromechanical parking brakes 168 a, 168 b and 568 a, 568 b maybe relatively slow acting, since it is necessary for output from themotor to be run through a reduction gear system to produce a sufficientbraking force with a motor of sufficiently small size and low weight.Thus, in normal operating situations, it is usual for the EPB-ECU 164 or164′ to be programmed such that it actuates the service brake actuatorvia valve actuator 166 to enable a fast brake application upon receivinga driver demand signal from the parking brake lever 170. This is thenfollowed by a signalling of the electromechanical parking brakes 168 aand 168 b for the longer term holding of the vehicle.

The system may also be provided with additional “hill-hold”functionality. A specific “hill-hold” button (not shown) may be providedfor the driver, e.g., on the parking brake lever. For holding tofunction, the vehicle engine must be running, the driver must be inplace (as detected by a seat-belt sensor for example), the vehicle mustbe at a standstill, and the ignition must be on. The function can beused to assist the driver to pull away on an incline without rollingbackwards, or as a precursor to full parking brake application. In somealternative implementations, the holding may be applied automaticallywhen the above conditions are met and released automatically when thedriver pulls away (“drive away function”) without the driver needing topress a button. The EPB-ECU 164 may also be configured such thathill-hold functionality times-out after being applied for apredetermined period of time. At this point, the full parking brake isapplied.

The EPB-ECU 164 or 164′ may also be configured to control the functionof a differential lock (not shown) in certain embodiments. As well as adifferential lock enabling a vehicle to have improved traction where onewheel on an axle has grip and another does not, it also enables thebrake torque of a functioning parking brake actuator to be transferredto a wheel on the same axle whose corresponding parking brake actuatorhas failed.

Furthermore, on vehicles having four or more driven wheels, additionaldifferential locks may be provided such that the brake torque fromfunctioning actuators on all driven wheels can be transferred to thewheel with the non-functioning actuator. Thus, such an arrangementenhances the failsafe nature of the system.

It is advantageous for this to be implemented by the EPB-ECU 164 ratherthan, for example, by the vehicle's EBS system. EBS systems aretypically rated to Automotive Safety Integrity Level (ASIL) C, whereasthe EPB-ECU is ASIL D capable (as defined by ISO WD 26262, level Dprovides the highest level of risk reduction, whereas level C is onelevel lower). The safety critical nature of the differential lock meansthat it is desirable for it to have ASIL-D control. Furthermore, theEPB-ECU 164 already has the functionality to monitor vehicle speed toensure the differential lock is only activated at low speeds (e.g., <7kph).

Typical brake application scenarios are shown in more detail in FIGS. 5and 6. In FIG. 5, the force application 210 corresponds to a driver ofthe vehicle pressing the “hill hold” switch 186 in the cab at time 211.Thus, the EPB-ECU 164 signals application of the service brake aircylinders 146 a and 146 b via the valve actuator 166, and a holdingforce F_(H) is achieved. When the driver then wishes to pull away, hereleases the park brake lever 170 or uses the drive away function, ifpresent, and the service brake is released. The EPB-ECU 164 isprogrammed to only permit hill-holding while the ignition is on (theignition switch sensor 193) and the driver is in his seat (the seatbeltswitch 195). If either of these conditions ceases to exist, the EPB-ECU164 signals application of the parking brakes 168 a and 168 b.

The force application 212 illustrates a holding phase instigated by thedriver at time 214 by applying the parking brake lever 170 at time 214.At time 216, the holding phase times-out, and the electrical actuationis starting to build up clamp force just electromechanically. However,this process may alternatively be automatic, such that if the driveractuates the “hill hold” switch 186 and the vehicle comes to standstill,the signal to the EPB-ECU 164 first triggers the holding phase followeda period thereafter by the parking phase in accordance with the logic ofthe EPB-ECU 164. In other embodiments, the force to go from the holdingforce F_(H) to a parking force F_(P) may be applied by just the servicebrakes 146 a or the service brake and electromechanical parking brakes168 a and 168 b together. This reduces the amount of energy requiredfrom the electromechanical parking brake

Once the required parking brake force has been achieved, the servicebrakes 146 a and 146 b are released, and the vehicle is held by theelectromechanical parking brakes 168 a and 168 b alone. Theelectromechanical parking brakes 168 a and 168 b are configured suchthat they are self locking, and no energy is required to maintain theparking brake force.

At time 218, the driver releases the parking brake lever 170 or uses thedrive away function, causing the EPB-ECU 164 to signal the back-drivingof the electromechanical parking brakes 168 a and 168 b, thus releasingthe parking brake and enabling the vehicle to be driven off.

Third force application 220 illustrates a scenario in which the airsupply system on the vehicle has failed. In this instance, theelectrical system remains operable and it is still possible to safelypark the vehicle by applying just the electromechanical parking brakes168 a and 168 b. At time 222, the driver applies the parking brake lever170, and the EPB-ECU 164, having been signalled that the air system isnon-functional via the CAN bus 173, follows an alternative process forthis scenario whereby the electromechanical parking brakes 168 a and 168b alone are applied. As can be seen by the gradient of the force line,full application of the parking brakes takes more time without theassistance of the service brakes 146 a and 146 b, but nevertheless thesame parking force F_(P) is ultimately achieved, and the vehicle may besafely parked.

FIG. 6 illustrates a further braking scenario in which the initialportion of the force application 224 corresponds largely to a forceapplication 212. However, in this scenario, the vehicle is parked on ahill, and the driver has required assistance from the “hill hold”system. At time 225, the vehicle comes to standstill. Alternatively, theEPB-ECU 164 can be programmed in that way that after the vehicle comesto rest at time 225, the hill hold will automatically be applied. Thisapplies the service brakes 146 a and 146 b. At time 226, the timeout orthe driver leaving his seat causes the electromechanical actuators toengage for parking. At time 228, the driver then releases the parkingbrake lever 170, causing the service brakes 146 a and 146 b to bere-applied to the holding force position and subsequently theelectromechanical parking brakes 168 a and 168 b to reduce to theholding force F_(H). The driver can then pull away without risking thevehicle rolling backwards by, at time 230, just by engaging drive orreleasing hill hold,

FIG. 7 illustrates an algorithm followed by the EPB-ECU 164, by whichthe holding force F_(H) and the parking force F_(P) may be adjusted byestimating the load or weight of the vehicle 101.

There are a number of ways by which the weight of the vehicle may beestimated, without including a large number of additional sensors on thevehicle. At step 310, the EPB-ECU 164 determines whether the vehicle istravelling at less than 10 kilometres per hour (by using signals fromwheel speed sensors 199). If yes, then at step 312, it determineswhether the vehicle is accelerating (again by using the wheel speedsensors) and if yes, determines the load of the vehicle at step 314 bycomparing values for engine torque (determined from torque sensor 196),achieved acceleration and incline (by using the inclinometer 190) toderive the value load_(A). The lower the acceleration for a giventorque, the greater the vehicle weight

If at step 310 the vehicle is travelling at greater than 10 kilometresper hour, or at step 312 it is not accelerating, the EPB-ECU 164determines at step 316 if the vehicle is braking from the brake pedalswitch 188. If no, the EPB-ECU 164 determines at step 318 whether airpressure is available, and if yes, derives load by using data from a theload sensitive brake force meter sensor 192 or from a sensor measuringair pressure in the air suspension system (not shown).

If at step 316 the EPB-ECU 164 determines that no braking is occurringand at step 318 no air pressure is available, the load is set toload_(MAX) at step 328 (i.e., the maximum gross vehicle weight). Ifbraking is occurring at step 316 a further value for the weight,load_(B) is determined from the sum values obtained for the brake torquefrom sensor 197, retarder torque from sensor 198, and engine brakingfrom engine torque sensor 196 in conjunction with deceleration fromwheel speed sensors 199 and inclinometer 190 at step 322.

Thereafter, at step 324, the EPB-ECU 164 determines which of loadsload_(A), loads and load_(B) is the largest. In its subsequentcalculations, it uses the largest value for safety reasons. Thisoperation may be carried out periodically and will collect values thathave been determined from steps 314, 320, and 322 within a certainpredetermined period of time in order to enhance the accuracy of theload estimation. Of course, since certain vehicles (e.g., road saltingtrucks or refuse trucks) will vary in weight while they are drivingalong, the period of validity of any particular calculated readingcannot be too long. The frequency with which step 324 is carried out andthe period of validity depends upon vehicle application, with aforesaidroad salting trucks and refuse trucks requiring higher frequency andlower validity periods than standard haulage/line-haul trucks.

If multiple values for the weight are available from steps 314, 320 and322, then at step 326 the validity of these weight calculations may bedetermined by averaging the calculated loads and checking whether any ofthese depart from this average value by more than a predetermined erroramount ΔX. If the load readings are not considered to be valid becausethe divergence is too great, then the load estimation may insteaddefault to the maximum gross vehicle weight for the greatest amount ofsafety.

Once the load has been estimated, this value can then be used inconjunction with signals from the inclinometer 190 to provide one set ofvalues that can be used by the EPB-ECU 164 to determine the forcerequired to hold or park the vehicle safely because heavier vehicles andsteeper inclines require a greater holding force from the parking brake.In addition, the weight or load is an important value for use insubsequent calculations to estimate brake component temperatures.

When estimating the temperature of a brake component, particularly thebrake discs 169 a and 169 b, it is desirable to determine the volume ofdisc because the smaller the volume of the disc, the more it will heatfor a given amount of energy imparted to it by the braking operation.This is particularly applicable for heavy vehicle brakes since over thelife of a brake disc, it may lose 6 kilograms or thereabouts in mass asit wears. Therefore, at the end of the life of the disc it will reach ahigher temperature for a given braking operation than when unworn. Inlight vehicles, the loss of mass as a proportion of starting weight isusually less significant and ignored by using the mass of worn discs.

FIG. 8 illustrates an algorithm for determining the volume of a brakedisc over its life. Thus, at step 330, the EPB-ECU 164 determines if thevehicle brakes are being applied to slow the vehicle. If yes, then abraking counter increments its value 1 higher at step 332. Then, at step334, a distance counter adds to the total distance traveled from thevelocity of the vehicle and the time since the algorithm last ran. Alimited amount of wear occurs to the brake disc even if no braking isoccurring, so it is important to monitor the total distance traveled fora particular disc. If no braking is occurring at this time, step 332 isskipped.

At step 336, the volume of the disc is determined by subtracting fromthe original volume V_(discoriginal) a value corresponding to thebraking counter times a factor K₁ corresponding to the average amount ofwear during a braking operation, and by further subtracting a valuecorresponding to the distance counter multiplied by a second factor K₂for the average wear of the disc during normal driving and which nobraking is occurring to provide a value for V_(disc). Typically, thealgorithm runs every hundred milliseconds in order to provide acontinuous value for the disc volume. The counters may be reset by adiagnostic program each time a disc is replaced. The algorithm runs forat least each disc that has a parking brake attached and may run for alldiscs in order to monitor wear, as well as for use in heat calculations.

An alternative embodiment for disc volume calculation employs continuousbrake pad wear sensors to derive a value for disc volume, as there is arelationship between pad wear and disc wear for given disc and padmaterials. However, since the service life of pads and discs varies,changes of both pads should be logged by a diagnostic program formeaningful volume data to be derived over the life of the brake.

Having determined the estimated weight of the vehicle and the volume ofeach brake disc, it is then possible to use these values in conjunctionwith values for the speed at the beginning and end of a brakingoperation, the density of the brake disc, the heat capacity of the brakedisc, the distribution of the brake force between the wheels of avehicle, and an empirically derived function relating to the proportionof energy entering the brake disc during operation in order to estimatethe increase in temperature of each brake disc of the vehicle duringthis operation.

This is achieved in accordance with the following equation:

${\Delta \; T_{+}} = \frac{B_{HA} \times f_{x} \times \frac{1}{2} \times \frac{1}{2}{m_{Fz}\left( {v_{start}^{2} - v_{end}^{2}} \right)}}{\rho \times c_{disc} \times V_{disc}}$

Where:

-   -   ΔT₊=the increase in temperature [° C.]    -   B_(HA)=the front to rear distribution of the brake force.    -   f_(x)=the portion of energy from the braking operation going        into the disc (typically ≈80%).    -   m_(Fz)=the estimated weight of the vehicle as determined by the        load estimation module [kg].    -   ρ=the density of the brake disc [kg/mm³].    -   c_(disc)=the heat capacity of the brake disc [J/(kg×K)]    -   V_(disc)=the calculated volume of the brake disc obtained from        the disc volume algorithm [mm³].        v_(start)=the vehicle speed at the beginning of the braking        operation [m/s]    -   v_(end)=the vehicle speed at the end of braking [m/s]

Where v_(end) is calculated according to the equation:

v _(end) =v _(start) −a _(Fz) ×t

Where:

-   -   a_(Fz)=the vehicle deceleration [m/s²] (also factoring in input        from the inclinometer for situations in which the vehicle is        driving down hill, but with a constant speed against the        influence of gravity).    -   t=time [s].

And where each axle comprises two brakes sharing the braking effortequally.

V_(start) and optionally v_(end) may be derived from the vehicle ABSsensor and/or the engine speed and the gear selection sensor. In apreferred embodiment, both are used with the higher of the two used forv_(start) and the lower for v_(end) in order to provide optimum safety.If v_(end) is obtained in this way, it need not be calculated using theequation above.

Thus, starting from the ambient temperature from temperature sensor 194(the default value may be set at 50° C., for example), the EPB-ECU 164can sum the temperature change of each brake application to determinethe temperature of the brake surface.

Of course, the brake disc will cool over time from an elevatedtemperature towards the ambient air temperature. The faster the vehicleis travelling, the greater the amount of cooling that will occur. Thus,in addition to the calculation of increases in temperature due tobraking following the temperature model set out above, it is alsonecessary to have a temperature model for the cooling of the brake.

This may be determined using the following equation:

${\Delta \; T_{-}} = {\left( {T_{disc} - T_{env}} \right) \times \left( {1 - ^{\frac{{- \Delta}\; t}{k_{v}}}} \right)}$

Where:

-   -   ΔT⁻=the decrease in temperature [° C.]    -   T_(disc)=the temperature of the brake disc [° C.]    -   T_(env)=ambient temperature [° C.]    -   e=the exponential constant    -   t=time [s]    -   k_(v)=a speed dependent cooling constant that is determined        using the following equation:

$k_{v} = \frac{\rho \times c_{disc} \times V_{disc}}{A_{disc} \times {k_{cool}(v)}}$

-   -   ρ=the density of the brake disc [kg/mm³].    -   c_(disc)=the heat capacity of the brake disc [J/(kg×K)]    -   V_(disc)=the calculated volume of the brake disc obtained from        the disc volume algorithm [mm³].    -   A_(disc)=the cooling surface of the brake disc [m²]    -   k_(cool)(v)=a speed dependent cooling curve that is specific to        the characteristics of a particular vehicle.

However, where Δt=20 milliseconds, it is possible to use theapproximation:

1−e ^(x) =x(|x<<1|)

such that the cooling may be calculated using the following simplifiedequation

${\Delta \; T_{-}} = {\left( {T_{disc} - T_{env}} \right) \times \left( \frac{{- \Delta}\; t}{k_{v}} \right)}$

Therefore, starting from a condition in which the brake disc of avehicle is at ambient air temperature, the temperature of the brake disccan be estimated at any time during the subsequent driving of thevehicle by employing the temperature model for the heating of the brakeswhen the brakes are applied and the temperature model for the cooling ofthe brake during free running of the vehicle.

As a result, when the vehicle driver wishes to park the vehicle, theEPB-ECU 164 has a value for the temperature of each brake disc on thevehicle that has a parking brake fitted.

From this temperature, it is possible to determine how much the brakedisc will shrink as it cools towards the ambient air temperature as thecoefficient of thermal expansion of the brake disc material is known.

Ignition off time will be considered as well and used for a coolingfunction without vehicle speed after the next ignition on as long as thevalues of the temperature model are above ambient temperature, and ifthis is not available, as long the values of the temperature model areabove the default value.

Turning now to FIGS. 9 and 10, the graphs of force versus time showntherein illustrate how knowledge of brake disc temperature and otherfactors such as the weight of the vehicle and incline may be used toalter the “hill hold” holding force F_(H) and the parking force F_(p).

In FIG. 9, the thicker lines on the force versus time graph correspondto the lines on the force application 212 of FIG. 5 and has beenlabelled generally 412 and includes a holding portion at which a holdingforce F_(H) is applied by the service brake actuator 146 a and 146 b anda parking force F_(P) at which a parking brake force is applied by theelectromechanical parking brake actuator 168 a and 168 b.

However, if the EPB-ECU 164 determines that the incline on which thevehicle is to be held during the holding phase is low and/or the load ofthe vehicle is low, then it signals the service brake actuators 146 a,146 b, 148 a, 148 b to apply a lower holding force F_(Hlow).

If a high gradient and high load is determined, then a higher holdingload F_(Hhigh) is signalled to the service brake actuators.

If a high gradient combined with a low load or a low gradient combinedwith a high load is detected, then the intermediate holding force F_(H)is still applied. As “holding” does not occur for significant periods oftime, it is unnecessary to consider the heat of the disc as a factor forthe holding force.

When the driver applies a park command, then a high gradient and highload or high temperature results in a higher parking force F_(Phigh)(e.g., 160 kN) being applied by the electromechanical parking brake 168a and 168 b.

However, if a low gradient and low load and low temperature is detected,then a lower force F_(Plow) (e.g., 80 kN) is applied by theelectromechanical parking brake 168 a and 168 b. The intermediate forceF_(P) (e.g., 120 kN) is similarly applied only if there is a highgradient and low load or low gradient and high load.

FIG. 10 differs from FIG. 9 in that rather than only three possible loadvalues being available for holding and parking, the loading may beadjusted linearly between the upper and lower limits anywhere within theshaded area of the graph, thereby allowing finer control of the brakeforces applied by the service and parking brake.

In circumstances where the parking brake is applied with a brake disc ata high temperature, a number of different approaches may be employed toensure that a secure parking of the vehicle may be achieved.

One possibility is (disclosed in FIGS. 9 and 10) applying a sufficientlyhigh force during parking initially such that even when the disc coolsand contracts, there is still a sufficient force to hold the vehicle.Alternatively, the EPB-ECU 164 may be programmed such that after apredetermined period of time, for example 30 minutes, it will signal thedriving of the electromechanical parking brakes 168 a and 168 b in orderto again provide a sufficiently high braking force to hold the vehicle.

In another alternative, the electromechanical parking brakes 168 a and168 b may be configured with a resilient element to take up thecontraction with a minimal reduction in clamp force.

Finally, and least desirably, the EPB-ECU 164 may simply provide awarning to the driver that the disc temperature is too high to guaranteea sufficient clamp force after cooling and that he or she must makealternative provision to ensure the vehicle is held (e.g., ensuring thata transmission lock is in place or that chocks are placed under thewheels).

The EPB-ECU 164 may also be programmed with a number of furtheralgorithms. For example, to account for the ageing of the calipermechanism and the electromechanical parking brakes 168 a and 168 b whichwould result in a greater internal frictional resistance to applicationof the parking brake, a counter may be provided within the EPB-ECU 164to count the number of ignition cycles, brake applications, park brakeapplications and ignition on time, and compensate for such wear.

The various factors influencing initial clamp force, compliance force(where a resilient element is present within the parking brake toaccount for contraction) or the amount of reclamp force to be appliedafter cooling are illustrated schematically in FIG. 12.

Furthermore, as a final safeguard against vehicle roll-away, the EPB-ECU164 may monitor the wheel speed sensors mounted on the wheels for theABS/EBS/ESP system of the vehicle to detect unexpected pulses therein.However, to enable the EPB-ECU 164 to react sufficiently quickly to aroll-away situation, the system should be configured to detect a singlepulse from the ABS/EBS control unit since the vehicle may otherwise havetoo great momentum to stop the roll-away by reapplication of the servicebrake.

ABS/EBS either are kept in operation after parking (independently fromignition status) or are reactivated in the critical time for roll away.They are configured to wake up the EPB ECU 164 for re-clamping.

The EPB-ECU 164 is preferably programmed with a test system that, whenused on vehicles including a tractor and trailer, enables the trailerbrakes to be released while the tractor parking brakes are applied. Thisenables the driver to check whether the tractor unit parking brakes arecapable of holding the combination without the trailer brakesfunctioning. This may be achieved by having a three position handbrakelever 170, which in addition to “off” and “applied” positions, also hasa “test” position for this purpose. The handle is pulled three times inthe test position to enter this test mode and exited by a single pull ora timeout of e.g., 10 seconds.

Alternatively, the lever may have a stable neutral position and unstable“off” and “applied” positions, with a plurality of user inputs into theapplied position causing the test mode to be entered, and a user inputinto the “off” position (or a timeout) causing the test mode to beexited.

Numerous changes may be made within the scope of the present invention.For example, the service brake valve actuator 166 may (together with aseparate valve) be separate from the service brake valve 140. In certainembodiments of the present invention, the surface temperature of thebrake discs may be measured directly by using a sliding temperaturesensor, e.g., a sliding negative temperature coefficient thermistor.

The foregoing description is only exemplary of the principles of theinvention. Many modifications and variations are possible in light ofthe above teachings. It is, therefore, to be understood that within thescope of the appended claims, the invention may be practiced otherwisethan using the example embodiments which have been specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

1. A system for adjusting a brake force to be applied by a brake, thesystem comprising: a module for estimating a weight of a vehicle towhich a brake is fitted; a module for determining an angle of inclineupon which the vehicle is positioned; and a control unit for calculatinga sufficient brake force to be applied according to predeterminedcriteria based upon the estimated weight and the angle of incline tomaintain the vehicle in a stationary state, the control unit beingconfigured to signal the brake to apply the calculated amount of force.2. The system according to claim 1, including a module for estimating atemperature of a brake component and configured to determine an amountof brake force required to maintain the vehicle in the stationary statebased upon a contraction of the brake component due the cooling of thebrake component from a temperature higher than ambient temperature oncethe component has reached the ambient temperature.
 3. The systemaccording to claim 2, configured to signal a further application of thebrake after a predetermined period if the system determines the brakeforce is insufficient to maintain the vehicle in the stationary state.4. The system according to claim 1, wherein the system is configured toapply a service brake to provide a hill hold function.
 5. The systemaccording to claim 1, wherein the system is configured to apply aparking brake.
 6. The system according to claim 2, wherein the modulefor estimating a temperature of a brake component is configured to usethe weight obtained by the module for estimating the weight of thevehicle to which the brake is fitted, the system including a volumeestimation module for estimating a volume of the brake component and atemperature model module for calculating a change in a temperatureduring brake application based on a relationship between the weight ofthe vehicle as estimated by the module for estimating the weight, thevolume of the brake component as estimated by the volume estimationmodule, deceleration of the vehicle, and further constants of at leastone of the vehicle and brake.
 7. The system according to claim 1,wherein the module for estimating the weight is configured to derive theweight of the vehicle from air pressure in an air suspension system ofthe vehicle or from a load sensitive regulating valve of a brake systemof the vehicle.
 8. The system according to claim 1, wherein the modulefor estimating the weight is configured to derive the weight of thevehicle by comparing a measurement of engine torque with vehicleacceleration.
 9. The system according to claim 1, wherein the module forestimating the weight is configured to derive the weight of the vehicleby estimating brake torque during braking.
 10. The system according toclaim 6, wherein the volume estimation module includes a counter todetect a duration of braking.
 11. The system according to claim 10,wherein the volume estimation module includes a counter of totaldistance traveled with the brake component in place in the vehicle. 12.The system according to claim 2, wherein the temperature model moduleuses a distribution of the brake force to calculate a temperature changeof the brake component.
 13. The system according to claim 2, wherein thetemperature model module uses a factor for a proportion of energyentering the brake component to calculate a temperature change of thebrake component.
 14. The system according to claim 2, wherein thetemperature model module uses data from the module for determining theangle of incline to calculate deceleration overcoming the effect ofgravity.
 15. The system according to claim 6, wherein the brakecomponent is a brake disc.
 16. The system according to claim 15, whereinthe volume estimation module uses a continuous brake pad wear sensoroutput to derive a value for the volume of the brake disc.
 17. A methodfor adjusting a brake force to be applied by a brake, the methodcomprising the steps of: (a) estimating a weight of a vehicle to which abrake is fitted; (b) determining an angle of incline upon which thevehicle is positioned; (c) calculating a sufficient brake force to beapplied according to predetermined criteria based upon the estimatedweight and the incline to maintain the vehicle in a stationary state;and (d) signalling the brake to apply the calculated amount of force.18. The method according to claim 17, further comprising the step ofestimating a temperature of the brake component preceding step (c), andstep (c) includes determining an amount of brake force required tomaintain the vehicle in the stationary state further based upon thecontraction of the brake component due the cooling of the component froma temperature higher than ambient temperature once the component hasreached the ambient temperature.
 19. The method according to claim 18,further comprising, after step (d), the step of signalling a furtherapplication of the brake after a predetermined time if the sufficientforce calculated at step (c) would no longer be sufficient to maintainthe vehicle in the stationary state.